Is JMicronATA.kext part of Yosemite? And others

There is a file JMicronATA.kext in my GF's iMac in /System/Library/Extensions ... is this an official part of OS X? Or can it be deleted? I ask because its modification date is 2012 and in System Report it shows that it's Not Signed and not loaded.

As well there are these kexts in /Library/Extensions which do not show to be from Apple, are not loaded, and many are from 2013:

ACS6x.kext AcrMSR.kext ATTOCelerityFC8.kext ATTOExpressSASHBA2.kext ATTOExpressSASRAID2.kext CalDigitHDProDrv.kext HighPointIOP.kext HighPointRR.kext PromiseSTEX.kext SoftRAID.kext

What are all these and why are they in /Library/Extensions instead of /System/Library/Extensions if they are officially part of OS X Yosemite? If they're not, how can I identify where they came from? Why would they still be there after I just reinstalled Yosemite yesterday?

How can you tell what's an official part of the system, and what isn't? How can you uninstall 3rd party crap, short of rooting out individual files from within alllll of the folders in the three different Library folders, not to mention anything hidden in the /private directory??

Thanks.